linux-hardening - Re: [PATCH v2 2/5] treewide: Replace open-coded flex arrays in unions

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Date:   Fri, 27 Aug 2021 09:08:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Kalle Valo <kvalo@...eaurora.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Luca Coelho <luciano.coelho@...el.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Mordechay Goodstein <mordechay.goodstein@...el.com>,
        Lee Jones <lee.jones@...aro.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
        linux-crypto@...r.kernel.org, ath10k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-can@...r.kernel.org,
        bpf@...r.kernel.org, Rasmus Villemoes <linux@...musvillemoes.dk>,
        Keith Packard <keithp@...thp.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        clang-built-linux@...glegroups.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 2/5] treewide: Replace open-coded flex arrays in unions

On Thu, Aug 26, 2021 at 08:24:52AM +0200, Marc Kleine-Budde wrote:
> On 25.08.2021 22:04:55, Kees Cook wrote:
> > In support of enabling -Warray-bounds and -Wzero-length-bounds and
> > correctly handling run-time memcpy() bounds checking, replace all
> > open-coded flexible arrays (i.e. 0-element arrays) in unions with the
> > flex_array() helper macro.
> > 
> > This fixes warnings such as:
> > 
> > fs/hpfs/anode.c: In function 'hpfs_add_sector_to_btree':
> > fs/hpfs/anode.c:209:27: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct bplus_internal_node[0]' [-Wzero-length-bounds]
> >   209 |    anode->btree.u.internal[0].down = cpu_to_le32(a);
> >       |    ~~~~~~~~~~~~~~~~~~~~~~~^~~
> > In file included from fs/hpfs/hpfs_fn.h:26,
> >                  from fs/hpfs/anode.c:10:
> > fs/hpfs/hpfs.h:412:32: note: while referencing 'internal'
> >   412 |     struct bplus_internal_node internal[0]; /* (internal) 2-word entries giving
> >       |                                ^~~~~~~~
> > 
> > drivers/net/can/usb/etas_es58x/es58x_fd.c: In function 'es58x_fd_tx_can_msg':
> > drivers/net/can/usb/etas_es58x/es58x_fd.c:360:35: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds]
> >   360 |  tx_can_msg = (typeof(tx_can_msg))&es58x_fd_urb_cmd->raw_msg[msg_len];
> >       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:22,
> >                  from drivers/net/can/usb/etas_es58x/es58x_fd.c:17:
> > drivers/net/can/usb/etas_es58x/es58x_fd.h:231:6: note: while referencing 'raw_msg'
> >   231 |   u8 raw_msg[0];
> >       |      ^~~~~~~
> > 
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Ayush Sawal <ayush.sawal@...lsio.com>
> > Cc: Vinay Kumar Yadav <vinay.yadav@...lsio.com>
> > Cc: Rohit Maheshwari <rohitm@...lsio.com>
> > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: Kalle Valo <kvalo@...eaurora.org>
> > Cc: Jakub Kicinski <kuba@...nel.org>
> > Cc: Stanislaw Gruszka <stf_xl@...pl>
> > Cc: Luca Coelho <luciano.coelho@...el.com>
> > Cc: "James E.J. Bottomley" <jejb@...ux.ibm.com>
> > Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Andrii Nakryiko <andrii@...nel.org>
> > Cc: Martin KaFai Lau <kafai@...com>
> > Cc: Song Liu <songliubraving@...com>
> > Cc: Yonghong Song <yhs@...com>
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: KP Singh <kpsingh@...nel.org>
> > Cc: Johannes Berg <johannes.berg@...el.com>
> > Cc: Mordechay Goodstein <mordechay.goodstein@...el.com>
> > Cc: Lee Jones <lee.jones@...aro.org>
> > Cc: Wolfgang Grandegger <wg@...ndegger.com>
> > Cc: Marc Kleine-Budde <mkl@...gutronix.de>
> > Cc: Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>
> > Cc: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> > Cc: Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
> > Cc: linux-crypto@...r.kernel.org
> > Cc: ath10k@...ts.infradead.org
> > Cc: linux-wireless@...r.kernel.org
> > Cc: netdev@...r.kernel.org
> > Cc: linux-scsi@...r.kernel.org
> > Cc: linux-can@...r.kernel.org
> > Cc: bpf@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  drivers/net/can/usb/etas_es58x/es581_4.h          |  2 +-
> >  drivers/net/can/usb/etas_es58x/es58x_fd.h         |  2 +-
> 
> For the can drivers:
> 
> Acked-by: Marc Kleine-Budde <mkl@...gutronix.de>

Thanks!

> BTW: Is there opportunity for conversion, too?
> 
> | drivers/net/can/peak_canfd/peak_pciefd_main.c:146:32: warning: array of flexible structures

Oh, hrmpf. This isn't a sane use of flex arrays:


struct __packed pucan_rx_msg {
	...
	__le32	can_id;
	u8	d[];
};

struct pciefd_rx_dma {
        __le32 irq_status;
        __le32 sys_time_low;
        __le32 sys_time_high;
        struct pucan_rx_msg msg[];
} __packed __aligned(4);

I think that needs to be handled separately. How are you building to get
that warning, by the way? I haven't seen that in my builds...

-- 
Kees Cook